The levels of specific cyclic GMP binding protein distinct from the cGMP kinase will be evaluated in a number of tissues including heart, aorta, pancreas, uterus, cerebellum and in fetal and neonatoal lung tissue at various stages in development. This investigation focuses on the elucidation of the biochemical characteristics of a cyclic GMP binding protein. The relationship of the binding protein to a cyclic GMP phosphodiesterase which co-purifies will be studied using a variety of techniques. The cyclic GMP binding protein will be purified to homogeneity and the molecular characteristics of this binding protein including amino acid composition, molecular weight and subunit structure will be determined. The stoichiometry of cyclic GMP binding and the mechanism by which 3-methylisobutyl-xanthine stimulates the cyclic GMP binding will be studied.